Method of producing fine powders



. r m a Patented .llan. 16, 1923. ll

unrreo STATES earner caries.

WARREN K. LEWIS, OF NEWTON, MASSACHUSETTS, ASSIGNOR TO THE GOODYEAR TIRE & RUBBER COMPANY, OF AKRON, OHIO, A. CORPORATION OF OHIO.

METHOD OF PRODUCING FINE POWDERS.

No Drawing. Application filed August 13, 1918. Serial No. 249,639.

T0,,lp/mmifmay concern: sible to produce a powder of a degree of ie it known that I, VVARRE. K. Lewis, fineness more nearly approaching the moa citizen of the United States, residing at lecular condition. At the same time, my Newton. in the county of Middlesex and process will usually efiect other. improve- 5 Slate of Massachusetts, have invented a new mentsas will be apparent from the followand useful Improvement in the Method of ing. Producing Fin Powders, of which the 101- V In brief, my invention resides in the- (lilowing is a specification. lution of the zinc vapors and oxygen with My invention relates to the art of prea very large proportion of inert gas, to the 10 During fine powders and will be fully unprimary end that the re-action between the derstood from the following specification. zinc and oxygen may take place in what It has long been recognized that powders may be described as a dilute gaseous soluprepared by subli'ming or precipitating tion. Under such circumstances, the molet'rom the gaseous state arev finer than those cules of zinc oxide as they are formed bv 15 prepared by any, mechanical grinding: the re-action, will be much more widely method. As an example, zinc white or zinc separated from one another, and further- 7 oxidemay be mentioned. This substance is more the heat of the re-action or comb-uscomnionly prepared. by roasting a Zinc ore tlon will be absorbed by the diluting atmosdirecth', with a, b d of carbonaceous fuel, phere. so that the temperature of the nascent 20 thereby effecting the simultaneous reducoxide will be very much reduced. There tionoi the ore and volatilization of the eleis evidence that both of these conditions mental zinc. The zinc vapors thus prowill contribute to retard the association of duced are led to a diffusion chamber in the individual molecules into large aggrewhich they are admixed with air. The zinc gates.

25 vapors here unite with or burn in the air. One of the improved results mentioned,

producing zinc oxide -in the form of an i. e., the reduction of temperature of the impalpable powder which is collected by re-action. may be further benefited by the filtration through dust bags. For the prosubstitution of a gas such as flue gas conduction of an especially pure and fine zinc taining carbon dioxide for a truly inert gas.

30 oxide. the process is modified to the extent The zinc vapors may here become oxidized that pure spelter is heated to the boiling by carbon dioxide. reducing the latter to the point in a retort, and the zinc vapors lead monoxide with a considerably smaller heat therefrom into the dii'iusion chamber where of re-action than would necessarily be dethev are burnt or oxidized. as above developed were the Zinc to combine directly 35 scribed. with free oxygen. 1

From theoretical considerations. it would In order to obtain the most advantageous appear that the Zinc oxide powder as origiresults from an operative standpoint. it may nally produced by either of these methods b desirable to introduce the diluting gas would approach a molecular condition of into the distilling retort where the zinc Va- 40 fineness since it is reasonable to suppose that pors are produced by direct distillation of the actual 'oxidation taking place in the pure spelter. Here the diluting gas current gaseous phase produces primarily single and will. in accordance with Daltons laws of separate molecules of zinc oxide. As colvapor pressure. effect the volatilization of lc ted. however. the powder, while very fine. the zinc at a temperature which may be 45 dces not by any means approach this movery much below the atmospheric boiling lecular ondition and in fact, it is only point of the zinc. This will reduce the wear by the greatest care and skill that a powder on the retort and will further benefit the may be obtained sufficiently fine for use in entire process since the zinc vapors, being the manufacture of high grade paints. It evolved at a lower temperature, will carry 50 is. therefore. apparent that after their forheat and in efi'ect. further lower the mation. the zinc oxide molecules rapidly astemperature in the diffusion chamber. It sociate into larger masses. i may be remarked that this last-named im- I have discovered that by a slight modiproved eil ect approaches the result obtainlication of the process described. it is posable by vacuum distillation. The same effeet is also obtainable by introducing the diluent gas into the reducing furnace, but the best results are secured by admitting it to the flue from that furnace in order to avoid the-slowing-up of the reduction by cooling.

It will be apparent that in accordance with the principles of the present invention, the degree of fineness of the resultant owder will be a function of the extent to which the dilution is carried out in the diffusion chamber. For. the production of a zincpowder of a degree of fineness suitable for the most exacting service which is now known, it is suggested that a dilution of from 100 to 200 volumes will be found proper. In general, the greater the degree of dilution, the finer the resultant product, with the practical limitation that too great dilution will involve an unduly large apparatus and may result in an increased percentage of loss of product.

As set forth above, a preferred process according to my invention, taking the production' of zinc oxide as an example, con'-.

sists in the introduction of 100 to 200 volumes of combustion gases (which may be the gases passing through the dust filters beyond the diffusion chamber, this re-use of the gases resulting in a saving of zinc loss). into the diffusion chamber, as by a blower or fan, a portion of such diluting gas being introduced with the zinc vapors and a portion with the air.

It will be apparent from the foregoing that the process above described as to its general features, is applicable to a wide variety of metallurgical processes involving the production of fine powders by subliming or condensing, or precipitating from the gaseous phase. Thus the process is applicable to the production of basic sulphite of lead or sublimed lead, the dilution being carried out just before or during precipitation. Arsenic and antimony sulphidles which are distilled from retorts for use as pigments or fillers may likewise be improved in quality in the same'manner. lit will be understood that while I have described in considerable detail a preferred method of carrying out my improvedprocess as applied to one specific-material, the invention is not to be regarded as limited to the detailed method described, except in so far as such limitations are included within the terms of the accompanying claims in which it is my intention to claim all noveity inher- 1. The improvement in the art of producing fine powders by precipitation from gases, which consists in bringing together the reacting gases under reacting conditions in the presence of a relatively large diluting volume of inert gas, whereby the precipi-v tated solid compound is secured in finely divided form.

2. The improvement in the art of producing fine powders by the oxidation of metallic vapors which consists in causing such oxidation to take place in a gaseous medium in which the oxygen content is relatively small.v

3. The improvement in the art of producing fine powders by the oxidation of metallic vapors which consists in carrying out the said oxidation in a gaseous medium consisting of a relatively small proportion of oxygen diluted with a relatively large proportion of combustion gas.

4. The improvement in the art of produc-- ing zinc oxide which consists in continuously introducing a relatively large proportion of inert gas into the diffusion chamber, whereby the oxidation of the zinc vapors takes place in a dilutegaseous medium.

'5'. The improvement in the artof producing zinc oxide which consists in introducing a relatively large volume of inert gas into the diffusion chamber and mixed with the air entering the said chamber.

6. The improvement in the art of producing zinc oxide which consists in introducing a relatively large volume of I combustion gases into the air entering the diffusion chamber.

I 7 The improvement in the art of producing zinc oxide by distillation of spelter which consists in introducing a relatively large volume of inert gas into the distillatory retort and causing said gas to mix with and pass into the diffusion chamber with the evolved zinc vapors.

8. The method of producing zinc oxide.

which consists in continuously reintroducing into the diffusion chamber arelatively large proportion of the gases passing from the said chamber.

\VARREN K. LEW Witness:

R. S. TWYNER. 

